RHIC progress and future Page: 5 of 7
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Figure 7: Effect of beam scrubbing on dynamic pressure
igre 7: ffe ct of b ca ie scr ing i eon . yn mi pFigure 9: M easured (red) and simulated transverse emit-
risetance evolution due to IBS, for a betatron phase advance of
82" (green) and 92" (blue) per FODO cell. Measured data
are for a phase advance of 92" per FODO cell.
Figure 8: Tomographic reconstruction of the longitudinal
phase space distribution of a RHIC bunch after the fast
transverse transition instability has occured.
of the longitudinal phase space shortly after the instability
This instability can be overcome by restoring Landau
damping with octupoles, and careful adjustment of the time
when the chromaticity crosses zero. For future improve-
ments, implementation of a fast chromaticity jump is under
IMPROVEMENTS WITH HEAVY IONS
IBS suppression lattice
Intrabeam-scattering (IBS) accounts for a significant lu-
minosity lifetime reduction in heavy ion collisions. The
emittance growth rates due to IBS can be calculated as
r 3 32 /2A
81 h r1C iA
I( . (2)
As Eq. (2) shows, the transverse emittance growth rate is
proportional to the "curly W" function,
rv + 2QDrD' + ;,D' a (3)
Reducing R therefore reduces the transverse emittance
growth due to IBS.
Figure 10: Effect of longitudinal stochastic cooling on Yel-
low beam lifetime.
This reduction is accomplished by increasing the betatron
phase advance per FOD)O cell from the nominal value of
o = 82< to 92<, and was implemented in the "Yellow"
RHIC ring during the Run-8 deuteron-gold run. Fig. 9
shows the gold beam measured emittance, together with
simulation results for phase advances of 82" and 921.
To compensate emittance growth of heavy ion beams clue
to IBS, a stochastic cooling system  is being installed
in RHIC. At present, longitudinal stochastic cooling is op-
erational in the "Yellow" RHIC ring. The lack of bunch
lengthening during stores results in longer beam lifetimes,
since no particles are lost from the RF bucket. Fig. 10
shows the beam intensity of stores with and without lon-
gitudinal stochastic cooling in the "Yellow" ring.
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Montag,C. RHIC progress and future, article, May 4, 2009; United States. (https://digital.library.unt.edu/ark:/67531/metadc934833/m1/5/: accessed May 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.